In vivo hydrogen peroxide diffusivity in brain tissue supports volume signaling activity.

Hydrogen peroxide is a major redox signaling molecule underlying a novel paradigm of cell function and communication. A role for HO as an intercellular signaling molecule and neuromodulator in the brain has become increasingly apparent, with evidence showing this biological oxidant to regulate neuronal polarity, connectivity, synaptic transmission and tuning of neuronal networks. This notion is supported by its ability to diffuse in the extracellular space, from source of production to target. It is, thus, crucial to understand extracellular HO concentration dynamics in the living brain and the factors which shape its diffusion pattern and half-life. To address this issue, we have used a novel microsensor to measure HO concentration dynamics in the brain extracellular matrix both in an ex vivo model using rodent brain slices and in vivo. We found that exogenously applied HO is removed from the extracellular space with an average half-life of t = 2.2 s in vivo. We determined the in vivo effective diffusion coefficient of HO to be D* = 2.5 × 10 cm s. This allows it to diffuse over 100 μm in the extracellular space within its half-life. Considering this, we can tentatively place HO within the class of volume neurotransmitters, connecting all cell types within the complex network of brain tissue, regardless of whether they are physically connected. These quantitative details of HO diffusion and half-life in the brain allow us to interpret the physiology of the redox signal and lay the pavement to then address dysregulation in redox homeostasis associated with disease processes.